1. Field of the Invention
The invention relates to a device for the burr-free cutting of strip-shaped material, especially made of metal, in two steps, which has two pairs of circular knives on axis-parallel knife shafts, each pair of circular knives consisting of a knife and a counter-knife, and by means of which the strip-shaped material is cut into by the first pair of circular knives in the first parting step and, in the second parting step, is severed in the opposite direction by the second pair of circular knives.
2. Discussion of the Prior Art
It is known to cut strip-shaped material, such as, for example, bands, sheets or the like, into individual strips by means of a pair of shears consisting of a knife and a counter-knife, that is to say a pair of knives. The knife and the counter-knife of the shears can be the knives of hydraulically or pneumatically operating shears or of eccentric shears, but also the circular knives of circular-knife or round-knife shears. Now when strip-shaped material is cut by means of such shears consisting of only a pair of knives, then, for example, a contraction occurs at the top edge of the material and burring occurs at the bottom edge. However, this burring particularly is disadvantageous to the further processing of the strip-shaped material, so that the material usually has to be retreated subsequently to remove the burr.
To avoid such a retreatment to remove the burr, which involves a high outlay in terms of the additional equipment required, German Auslegeschrift No. 1,806,305 discloses a process for burr-free cutting, in which the parting operation takes place in two steps. This is carried out by first cutting or shearing into the strip-shaped material from one side over some of the thickness of the material in the first parting step and subsequently, in the second parting step, severing it from the other side in the opposite direction until it is finally parted. As a result of this double shearing or cutting in opposite directions (counter-cut), burr-free cutting is achieved.
In the device known from German Auslegeschrift No. 1,806,305, the two parting steps consist of two pairs of circular knives, each pair with two pivot axles arranged axis-parallel, the two pairs being arranged in succession in the direction of the strip-shaped material to be severed. This known device therefore has two pairs of circular knives with a total of four axis-parallel knife shafts arranged successively in pairs. Here, the four circular knives are rigid circular discs consisting especially of a cutting steel. Burr-free cutting by means of this known device is carried out by first introducing the strip-shaped material into the first parting step with the first pair of circular knives, but only shearing into it in this step. A precondition for this is that the sum of the radii of the two circular knives of this first pair of circular knives be less than the distance between the two associated axis-parallel pivot axles or knife shafts. After it has left the first parting step, the strip-shaped material, which has only been cut into, subsequently enters the second parting step with the second pair of circular knives and is now severed completely in the opposite direction.
Although burr-free cutting of strip-shaped material is basically possible by means of this device known from German Auslegeschrift No. 1,806,305, nevertheless an essential disadvantage of this device is that the four knife shafts of the two pairs of circular knives have to be aligned exactly axis-parallel. This applies particularly to the two pairs of knife shafts arranged at a certain distance from one another in the first and second parting steps. It is necessary to align exactly axis-parallel not only the two knife shafts of the first and second parting steps relative to one another, but also the knife shafts of the first parting step relative to the two knife shafts of the second parting step. Thus, for example as a result of inaccurate alignment of the two pairs of knife shafts relative to one another, it can happen that the shearing or cutting plane defined by the second pair of circular knives (perpendicular relative to the surface of the strip-shaped material) does not coincide with the cutting plane of the first pair of circular knives. Only if this condition is satisfied, that is to say if the two cutting planes coincide, is it possible to make a burr-free right-angled cut.
Furthermore, another essential disadvantage of this known device is that the strip-shaped material has to be guided as exactly as possible between the two pairs of circular knives arranged in succession. Even when the strip-shaped material tilts only slightly between the pairs of circular knives, it can happen that the shearing or cutting plane of the second pair of circular knives is not met exactly by the strip cut into by the first pair of circular knives. It is then no longer possible to obtain a clean, burr-free and right-angled cut.
Starting from this state of the art, the object on which the invention is based is to provide a device of the type mentioned in the introduction, in which the strip-shaped material is prevented from tilting between the two pairs of circular knives and which allows burr-free right-angled cutting of the strip-shaped material.